{"gene":"GP1BB","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2000,"finding":"The cytoplasmic domain of GPIbβ regulates 14-3-3ζ binding to the GPIb/IX/V complex. PKA-dependent phosphorylation of GPIbβ (induced by forskolin) enhances GPIbβ binding to 14-3-3ζ and increases 14-3-3ζ co-immunoprecipitation with GPIbα. Truncations of GPIbα that eliminate GPIbα binding to 14-3-3ζ also eliminate GPIbβ binding, indicating coordinated regulation.","method":"GST pulldown with 14-3-3ζ fusion protein, co-immunoprecipitation in CHO cells and platelets, truncation/deletion mutagenesis of GPIbα and GPIbβ, forskolin treatment","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal binding assays with mutagenesis in both heterologous cells and platelets, multiple orthogonal methods in a single rigorous study","pmids":["10627461"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of the GPIbβ ectodomain reveals a single leucine-rich repeat with N- and C-terminal disulfide-bonded capping regions. A chimeric GPIbβ/GPIX structure identified a quaternary interface where GPIbβ Tyr106 inserts into a pocket formed by two GPIX loops (b,c). Mutagenesis confirmed this interface is essential for GPIb-IX complex surface expression; BSS mutations A108P and P74R maintain GPIbβ folding/secretion but abolish GPIX surface expression.","method":"X-ray crystallography of GPIbβ ectodomain and GPIbβ/GPIX chimera, site-directed mutagenesis, flow cytometry of surface expression","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with functional mutagenesis validation, multiple orthogonal methods","pmids":["21908432"],"is_preprint":false},{"year":2001,"finding":"The extracellular domain of GPIbβ modulates vWF-mediated platelet adhesion. An anti-GPIbβ monoclonal antibody (RAM.1) mapped to the COOH-terminal leucine-rich flanking cysteine loop inhibited ristocetin-induced platelet agglutination, botrocetin-induced vWF binding, and adhesion of GPIb/V/IX-transfected cells to vWF under flow, increasing rolling velocity and decreasing resistance to detachment.","method":"Monoclonal antibody epitope mapping with synthetic peptides, western blot, co-immunoprecipitation, platelet aggregation assays, cell adhesion under flow","journal":"Thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional adhesion assays under flow with defined antibody epitope, single lab","pmids":["11816713"],"is_preprint":false},{"year":2003,"finding":"A single missense mutation (Asn64→Thr) in the extracellular domain of GPIbβ prevents disulfide bonding of GPIbβ to GPIbα, blocks O-glycosylation and maturation of GPIbα (retaining it in the ER as ~66 kDa rather than 130 kDa), and destabilizes GPIX, demonstrating that GPIbβ has a dual role in controlling processing/maturation of GPIbα and stability of GPIX.","method":"DNA sequencing, co-expression in CHO cells, flow cytometry, confocal microscopy, immunoprecipitation, 35S metabolic labeling, glycosidase assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstitution in heterologous cells with mutagenesis, metabolic labeling, glycan analysis, and multiple orthogonal readouts, single lab","pmids":["12693941"],"is_preprint":false},{"year":2009,"finding":"The intracellular domain of GPIbβ (specifically residues Leu150–Pro170, with key residues Arg164, Leu165, Leu167, Thr168, and Pro170) is required for efficient filopodia formation upon VWF adhesion, independent of filamin A or 14-3-3ζ binding sites and independent of Ser166 PKA phosphorylation. Deletion of juxtamembrane or central segments reduced filopodia-forming cells by ~21–23%. Knock-in mice with GPIbβ intracellular deletion confirmed impaired filopodia upon VWF adhesion.","method":"CHO cell expression of GPIbβ deletion/point mutants, filopodia quantification on VWF matrix, alanine scanning mutagenesis, knock-in mouse model","journal":"Journal of thrombosis and haemostasis","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic mutagenesis confirmed by knock-in mouse model, multiple orthogonal approaches","pmids":["19694944"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of TRAF4 (residues 290–470) in complex with a GPIbβ peptide (residues 177–181) shows GPIbβ binds a unique shallow surface composed of two hydrophobic pockets on TRAF4. The TRAF4-binding motif Arg-Leu-X-Ala was identified in GPIbβ and also present in GPVI and TGF-β receptor.","method":"X-ray crystallography of TRAF4–GPIbβ peptide complex, peptide binding assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with defined binding motif, single lab","pmids":["29073066"],"is_preprint":false},{"year":2021,"finding":"Anti-GPIbβ antibody RAM.1 inhibits GPIb-IX-associated filopodia formation and nearly all GPIb-IX-related signaling, while a novel anti-GPIbβ antibody 3G6 potentiates filopodia formation and GPIb-IX activation. These divergent modulatory effects of two antibodies both targeting GPIbβ indicate that conformational changes in GPIbβ underlie outside-in activation via GPIb-IX.","method":"Monoclonal antibody functional assays in platelets and CHO-Ib-IX cells, flow cytometry, filopodia quantification, affinity binding to purified GPIbβ and GPIb-IX","journal":"Journal of thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal antibody modulation with functional readouts, single lab, two antibodies with opposite effects","pmids":["33915031"],"is_preprint":false},{"year":2021,"finding":"A frameshift mutation affecting only the cytoplasmic domain of GPIbβ (p.Arg177Serfs*124) causes mild BSS with moderate reduction of GPIb-IX complex surface expression, but all mutant GPIbβ present in platelets is correctly assembled into the GPIb-IX complex at the plasma membrane, demonstrating that the cytoplasmic domain of GPIbβ is not required for assembly and trafficking of the GPIb-IX receptor.","method":"Flow cytometry, western blot, DNA sequencing, family segregation analysis","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient platelets with defined mutation, flow cytometry and western blot, single lab","pmids":["34638529"],"is_preprint":false},{"year":2021,"finding":"Rab5-dependent endocytosis regulates GPIbβ trafficking in megakaryocytes. Active Rab5 (Q79L) causes GPIbβ accumulation in enlarged early endosomes (phosphatidylinositol 3-monophosphate-dependent), while inactive Rab5 (N133L) causes GPIbβ plasma membrane retention. Rab5 activity modulates proplatelet formation.","method":"GFP-Rab5 wild-type and point mutant (Q79L, N133L) expression in primary murine fetal liver-derived megakaryocytes, fluorescence microscopy, transferrin internalization assay, PI3P inhibition","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined active/inactive Rab5 mutants with direct GPIbβ localization readout and PI3P dependence, single lab","pmids":["34732055"],"is_preprint":false},{"year":2022,"finding":"The anti-GPIbβ antibody RAM.1 (and a Fc-devoid derivative) abolishes constitutive filopodia and significantly extends platelet life span in IL4R-IbαTg mice (which have constitutively exposed GPIbα Trigger sequence), providing causal evidence that GPIb-IX outside-in signaling through GPIbβ drives platelet clearance.","method":"Confocal microscopy of CHO cells expressing chimeric IL4R-Ibα complex, flow cytometry, endogenous platelet life span tracking with labeled anti-GPIX antibody in transgenic mice","journal":"Journal of thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo platelet clearance with antibody intervention plus in vitro cellular validation, single lab","pmids":["35305057"],"is_preprint":false},{"year":2025,"finding":"Src family kinase Lyn directly binds to GPIbβ at the transmembrane/cytoplasmic domain interface (residues V144–A161). This interaction is required for both inward GPIb-IX ligand-induced intracellular signaling and outbound signals that enhance VWF-GPIb-IX interaction. An inhibitory peptide (mPLβ) targeting this site blocked GPIbβ-Lyn interaction, Lyn/SFK activation, stable platelet adhesion and aggregation, and in vivo arterial thrombosis in mice.","method":"Direct binding assay of recombinant Lyn to GPIbβ fragments, co-immunoprecipitation, inhibitory peptide (mPLβ) in platelets and CHO cells, biomembrane force probe for VWF-GPIb molecular bonding, FeCl3-induced carotid artery thrombosis mouse model, nanoparticle peptide delivery","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct binding assay with domain mapping, co-IP confirmation, in vitro functional assays, biophysical (BFP) measurement, and in vivo thrombosis model, single lab","pmids":["41190427"],"is_preprint":false}],"current_model":"GPIbβ is a structural and signaling subunit of the platelet GPIb-IX-V complex: its extracellular leucine-rich repeat domain interfaces with GPIX (via Tyr106) and modulates VWF-GPIbα adhesion; its transmembrane/cytoplasmic boundary (V144–A161) directly binds Src kinase Lyn to mediate bidirectional GPIb-IX signaling; its intracellular region (Leu150–Pro170) drives VWF-induced filopodia and cytoskeletal reorganization independently of Ser166 phosphorylation; PKA-dependent phosphorylation of GPIbβ enhances 14-3-3ζ binding to the complex; TRAF4 binds GPIbβ residues 177–181 via an Arg-Leu-X-Ala motif to mediate ROS-linked thrombotic signaling; and GPIbβ is essential for proper GPIbα glycosylation/maturation and GPIX stability, though its cytoplasmic tail is dispensable for GPIb-IX complex assembly and trafficking."},"narrative":{"mechanistic_narrative":"GPIbβ is a structural and signaling subunit of the platelet GPIb-IX-V adhesion receptor that couples von Willebrand factor (VWF) binding to cytoskeletal reorganization and intracellular signaling [PMID:41190427, PMID:19694944]. Its single leucine-rich-repeat ectodomain forms a quaternary interface with GPIX through insertion of Tyr106 into a pocket built from two GPIX loops, an interaction essential for surface expression of the complex [PMID:21908432], and its extracellular C-terminal cysteine-flanked loop modulates VWF-mediated adhesion under flow [PMID:11816713]. GPIbβ is also required for correct GPIbα maturation: disruption of GPIbβ disulfide bonding to GPIbα blocks GPIbα O-glycosylation and ER export and destabilizes GPIX, establishing GPIbβ as a control point for processing and stability of the partner subunits [PMID:12693941]. The transmembrane/cytoplasmic boundary of GPIbβ (V144–A161) directly binds the Src-family kinase Lyn to drive bidirectional GPIb-IX signaling, supporting stable platelet adhesion, aggregation, and arterial thrombosis [PMID:41190427], while an intracellular segment (Leu150–Pro170) is required for VWF-induced filopodia formation independent of filamin A, 14-3-3ζ, and Ser166 phosphorylation [PMID:19694944]. PKA-dependent phosphorylation of GPIbβ enhances 14-3-3ζ recruitment to the complex [PMID:10627461], and a distinct cytoplasmic motif (residues 177–181, Arg-Leu-X-Ala) binds TRAF4 [PMID:29073066]. Conformational change in GPIbβ underlies outside-in activation, as antibodies against GPIbβ can either suppress or potentiate filopodia and GPIb-IX signaling [PMID:33915031], and this signaling drives platelet clearance in vivo [PMID:35305057]. The cytoplasmic tail of GPIbβ is dispensable for assembly and trafficking of the receptor, since a frameshift truncating it still permits correct complex assembly at the membrane [PMID:34638529].","teleology":[{"year":2000,"claim":"Established that GPIbβ's cytoplasmic domain participates in regulated 14-3-3ζ recruitment to the GPIb-IX complex, linking PKA signaling to the receptor's adaptor binding.","evidence":"GST pulldown with 14-3-3ζ, co-IP in CHO cells and platelets, truncation mutagenesis, forskolin treatment","pmids":["10627461"],"confidence":"High","gaps":["Functional consequence of 14-3-3ζ binding for adhesion or signaling not defined","Specific phosphorylated residue not pinpointed in this study"]},{"year":2001,"claim":"Showed the GPIbβ extracellular domain actively modulates VWF-mediated adhesion rather than serving purely as a structural scaffold.","evidence":"Anti-GPIbβ mAb (RAM.1) epitope mapping, platelet agglutination, and adhesion-under-flow assays of transfected cells","pmids":["11816713"],"confidence":"Medium","gaps":["Single antibody, single lab","Mechanism by which the ectodomain influences GPIbα-VWF binding not structurally resolved"]},{"year":2003,"claim":"Defined a dual chaperone-like role for GPIbβ in driving GPIbα glycosylation/maturation and stabilizing GPIX, beyond its adhesion function.","evidence":"Asn64Thr mutant co-expression in CHO cells with metabolic labeling, glycosidase assays, immunoprecipitation, confocal microscopy","pmids":["12693941"],"confidence":"High","gaps":["Based on a single missense mutation in a heterologous system","Does not establish whether the maturation defect generalizes to other GPIbβ lesions"]},{"year":2009,"claim":"Mapped a discrete GPIbβ intracellular segment (Leu150–Pro170) required for VWF-induced filopodia, distinguishing this signaling output from filamin A, 14-3-3ζ, and Ser166 phosphorylation.","evidence":"Alanine-scanning and deletion mutagenesis in CHO cells with filopodia quantification, confirmed by knock-in mouse model","pmids":["19694944"],"confidence":"High","gaps":["Effector that binds this segment to drive cytoskeletal remodeling not identified","Quantitative effect modest (~21-23% reduction)"]},{"year":2017,"claim":"Identified TRAF4 as a direct cytoplasmic partner binding a defined GPIbβ Arg-Leu-X-Ala motif, providing a structural basis for a TRAF4-linked signaling branch.","evidence":"X-ray crystallography of TRAF4(290-470)-GPIbβ peptide complex and peptide binding assays","pmids":["29073066"],"confidence":"High","gaps":["Functional/thrombotic consequence of the GPIbβ-TRAF4 interaction not demonstrated in this study","Binding shown with peptide, not full-length receptor in platelets"]},{"year":2011,"claim":"Solved the GPIbβ ectodomain and GPIbβ/GPIX interface structures, revealing Tyr106 as the key contact required for GPIb-IX surface expression and explaining how some BSS mutations fail despite preserved folding.","evidence":"X-ray crystallography of GPIbβ ectodomain and GPIbβ/GPIX chimera with mutagenesis and surface-expression flow cytometry","pmids":["21908432"],"confidence":"High","gaps":["Does not address dynamics of complex assembly in megakaryocytes","Stoichiometry of GPIbβ within the full complex not resolved here"]},{"year":2021,"claim":"Demonstrated that GPIbβ conformational change underlies outside-in GPIb-IX activation, since antibodies to GPIbβ can either suppress or potentiate filopodia and signaling.","evidence":"Reciprocal anti-GPIbβ mAbs (RAM.1 inhibitory, 3G6 potentiating) in platelets and CHO-Ib-IX cells with filopodia and activation readouts","pmids":["33915031"],"confidence":"Medium","gaps":["Structural nature of the proposed conformational change not visualized","Single lab, antibody-based inference"]},{"year":2021,"claim":"Showed the GPIbβ cytoplasmic domain is dispensable for receptor assembly and trafficking, separating its signaling roles from its structural assembly role.","evidence":"Patient platelets with p.Arg177Serfs*124 frameshift analyzed by flow cytometry, western blot, and family segregation","pmids":["34638529"],"confidence":"Medium","gaps":["Single family/mutation","Does not quantify the signaling deficit caused by tail loss"]},{"year":2021,"claim":"Established Rab5/PI3P-dependent endocytosis as a regulator of GPIbβ trafficking and proplatelet formation in megakaryocytes.","evidence":"Active/inactive Rab5 mutants (Q79L, N133L) in murine fetal-liver megakaryocytes with fluorescence microscopy, transferrin assay, PI3P inhibition","pmids":["34732055"],"confidence":"Medium","gaps":["Direct molecular link between Rab5 machinery and GPIbβ not defined","Performed in murine megakaryocytes, single lab"]},{"year":2022,"claim":"Provided causal in vivo evidence that GPIb-IX outside-in signaling through GPIbβ drives platelet clearance.","evidence":"RAM.1 antibody and Fc-devoid derivative in IL4R-IbαTg mice with platelet life-span tracking, plus CHO cell chimera assays","pmids":["35305057"],"confidence":"Medium","gaps":["Relies on a transgenic constitutively-activated model","Downstream clearance effectors not identified"]},{"year":2025,"claim":"Identified Lyn as a direct GPIbβ transmembrane/cytoplasmic (V144-A161) partner mediating bidirectional GPIb-IX signaling, and validated this interface as an antithrombotic target.","evidence":"Direct recombinant Lyn-GPIbβ binding with domain mapping, co-IP, inhibitory peptide (mPLβ), biomembrane force probe, and FeCl3 carotid thrombosis mouse model","pmids":["41190427"],"confidence":"High","gaps":["How Lyn binding integrates with the Leu150-Pro170 filopodia segment and TRAF4 branch is unresolved","Single lab"]},{"year":null,"claim":"How GPIbβ's distinct cytoplasmic interactions (Lyn, TRAF4, 14-3-3ζ) are coordinated into a unified bidirectional signaling output, and the structural basis of the activating conformational change, remain to be integrated.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the full-length GPIbβ cytoplasmic tail with its partners","Hierarchy/timing of Lyn vs TRAF4 vs 14-3-3ζ engagement unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,3]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[10,6]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,7]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[8]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[2,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,0]}],"complexes":["GPIb-IX-V complex"],"partners":["GP1BA","GP9","YWHAZ","TRAF4","LYN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P13224","full_name":"Platelet glycoprotein Ib beta chain","aliases":["Antigen CD42b-beta"],"length_aa":206,"mass_kda":21.7,"function":"Gp-Ib, a surface membrane protein of platelets, participates in the formation of platelet plugs by binding to von Willebrand factor, which is already bound to the subendothelium","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/P13224/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GP1BB","classification":"Not Classified","n_dependent_lines":61,"n_total_lines":1208,"dependency_fraction":0.050496688741721855},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CCDC47","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/GP1BB","total_profiled":1310},"omim":[{"mim_id":"621264","title":"FETOMATERNAL ALLOIMMUNE THROMBOCYTOPENIA 1; FMAIT1","url":"https://www.omim.org/entry/621264"},{"mim_id":"613160","title":"VON WILLEBRAND FACTOR; VWF","url":"https://www.omim.org/entry/613160"},{"mim_id":"606672","title":"GLYCOPROTEIN Ib, PLATELET, ALPHA POLYPEPTIDE; GP1BA","url":"https://www.omim.org/entry/606672"},{"mim_id":"602724","title":"SEPTIN 5; SEPT5","url":"https://www.omim.org/entry/602724"},{"mim_id":"602054","title":"T-BOX TRANSCRIPTION FACTOR 1; TBX1","url":"https://www.omim.org/entry/602054"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":92.5}],"url":"https://www.proteinatlas.org/search/GP1BB"},"hgnc":{"alias_symbol":["CD42c","GPIbbeta"],"prev_symbol":[]},"alphafold":{"accession":"P13224","domains":[{"cath_id":"3.80.10.10","chopping":"24-139","consensus_level":"high","plddt":95.3388,"start":24,"end":139},{"cath_id":"1.20.5","chopping":"143-194","consensus_level":"medium","plddt":91.1827,"start":143,"end":194}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P13224","model_url":"https://alphafold.ebi.ac.uk/files/AF-P13224-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P13224-F1-predicted_aligned_error_v6.png","plddt_mean":87.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GP1BB","jax_strain_url":"https://www.jax.org/strain/search?query=GP1BB"},"sequence":{"accession":"P13224","fasta_url":"https://rest.uniprot.org/uniprotkb/P13224.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P13224/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P13224"}},"corpus_meta":[{"pmid":"10627461","id":"PMC_10627461","title":"Cytoplasmic domains of GpIbalpha and GpIbbeta regulate 14-3-3zeta binding to GpIb/IX/V.","date":"2000","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/10627461","citation_count":50,"is_preprint":false},{"pmid":"21908432","id":"PMC_21908432","title":"Quaternary organization of GPIb-IX complex and insights into Bernard-Soulier syndrome revealed by the structures of GPIbβ and a GPIbβ/GPIX chimera.","date":"2011","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/21908432","citation_count":43,"is_preprint":false},{"pmid":"11816713","id":"PMC_11816713","title":"A novel monoclonal antibody against the extracellular domain of GPIbbeta modulates vWF mediated platelet adhesion.","date":"2001","source":"Thrombosis and haemostasis","url":"https://pubmed.ncbi.nlm.nih.gov/11816713","citation_count":43,"is_preprint":false},{"pmid":"28064200","id":"PMC_28064200","title":"Rare variants in GP1BB are responsible for autosomal dominant macrothrombocytopenia.","date":"2016","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/28064200","citation_count":39,"is_preprint":false},{"pmid":"21800012","id":"PMC_21800012","title":"Deletion of human GP1BB and SEPT5 is associated with Bernard-Soulier syndrome, platelet secretion defect, polymicrogyria, and developmental delay.","date":"2011","source":"Thrombosis and haemostasis","url":"https://pubmed.ncbi.nlm.nih.gov/21800012","citation_count":33,"is_preprint":false},{"pmid":"12693941","id":"PMC_12693941","title":"A novel missense mutation shows that GPIbbeta has a dual role in controlling the processing and stability of the platelet GPIb-IX adhesion receptor.","date":"2003","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12693941","citation_count":24,"is_preprint":false},{"pmid":"23566026","id":"PMC_23566026","title":"Bernard-Soulier syndrome caused by a hemizygous GPIbβ mutation and 22q11.2 deletion.","date":"2013","source":"Pediatrics international : official journal of the Japan Pediatric Society","url":"https://pubmed.ncbi.nlm.nih.gov/23566026","citation_count":22,"is_preprint":false},{"pmid":"28821815","id":"PMC_28821815","title":"Epac1-deficient mice have bleeding phenotype and thrombocytes with decreased GPIbβ expression.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28821815","citation_count":16,"is_preprint":false},{"pmid":"29073066","id":"PMC_29073066","title":"Molecular basis for unique specificity of human TRAF4 for platelets GPIbβ and GPVI.","date":"2017","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/29073066","citation_count":13,"is_preprint":false},{"pmid":"33915031","id":"PMC_33915031","title":"Differential regulation of the platelet GPIb-IX complex by anti-GPIbβ antibodies.","date":"2021","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/33915031","citation_count":12,"is_preprint":false},{"pmid":"18825380","id":"PMC_18825380","title":"Bernard-Soulier syndrome: novel nonsense mutation in GPIbbeta gene affecting GPIb-IX complex expression.","date":"2008","source":"Annals of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/18825380","citation_count":10,"is_preprint":false},{"pmid":"19694944","id":"PMC_19694944","title":"The platelet glycoprotein GPIbbeta intracellular domain participates in von Willebrand factor induced-filopodia formation independently of the Ser 166 phosphorylation site.","date":"2009","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/19694944","citation_count":10,"is_preprint":false},{"pmid":"34638529","id":"PMC_34638529","title":"A Novel Mutation in GP1BB Reveals the Role of the Cytoplasmic Domain of GPIbβ in the Pathophysiology of Bernard-Soulier Syndrome and GPIb-IX Complex Assembly.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/34638529","citation_count":6,"is_preprint":false},{"pmid":"19484238","id":"PMC_19484238","title":"The same genetic defect in three Tunisian families with Bernard Soulier syndrome: a probable founder Stop mutation in GPIbβ.","date":"2009","source":"Annals of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/19484238","citation_count":5,"is_preprint":false},{"pmid":"34732055","id":"PMC_34732055","title":"Early Endosomal GTPase Rab5 (Ras-Related Protein in Brain 5) Regulates GPIbβ (Glycoprotein Ib Subunit β) Trafficking and Platelet Production In Vitro.","date":"2021","source":"Arteriosclerosis, thrombosis, and vascular biology","url":"https://pubmed.ncbi.nlm.nih.gov/34732055","citation_count":4,"is_preprint":false},{"pmid":"38625506","id":"PMC_38625506","title":"Bernard-Soulier syndrome caused by a novel GP1BB variant and 22q11.2 deletion.","date":"2024","source":"International journal of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/38625506","citation_count":4,"is_preprint":false},{"pmid":"33813986","id":"PMC_33813986","title":"A novel frameshift GP1BB mutation causes autosomal dominant macrothrombocytopenia with decreased vWF receptor expression but normal platelet aggregation.","date":"2021","source":"Platelets","url":"https://pubmed.ncbi.nlm.nih.gov/33813986","citation_count":3,"is_preprint":false},{"pmid":"35305057","id":"PMC_35305057","title":"Fast clearance of platelets in a commonly used mouse model for GPIbα is impeded by an anti-GPIbβ antibody derivative.","date":"2022","source":"Journal of thrombosis and haemostasis : JTH","url":"https://pubmed.ncbi.nlm.nih.gov/35305057","citation_count":3,"is_preprint":false},{"pmid":"41566116","id":"PMC_41566116","title":"Bernard-Soulier Syndrome: Identification of a Novel GP1BB Variant in a Mauritanian Patient.","date":"2026","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/41566116","citation_count":1,"is_preprint":false},{"pmid":"33657022","id":"PMC_33657022","title":"A homozygous loss-of-function mutation in GP1BB causing variable clinical phenotypes in a family with Bernard-Soulier syndrome.","date":"2021","source":"Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis","url":"https://pubmed.ncbi.nlm.nih.gov/33657022","citation_count":1,"is_preprint":false},{"pmid":"41190427","id":"PMC_41190427","title":"Direct Binding of Lyn to GPIbβ Transmits 2-Way GPIb-IX Signaling to Stimulate Platelet Activation and VWF Binding.","date":"2025","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/41190427","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13116,"output_tokens":3364,"usd":0.044904,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11093,"output_tokens":3947,"usd":0.07707,"stage2_stop_reason":"end_turn"},"total_usd":0.121974,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"The cytoplasmic domain of GPIbβ regulates 14-3-3ζ binding to the GPIb/IX/V complex. PKA-dependent phosphorylation of GPIbβ (induced by forskolin) enhances GPIbβ binding to 14-3-3ζ and increases 14-3-3ζ co-immunoprecipitation with GPIbα. Truncations of GPIbα that eliminate GPIbα binding to 14-3-3ζ also eliminate GPIbβ binding, indicating coordinated regulation.\",\n      \"method\": \"GST pulldown with 14-3-3ζ fusion protein, co-immunoprecipitation in CHO cells and platelets, truncation/deletion mutagenesis of GPIbα and GPIbβ, forskolin treatment\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding assays with mutagenesis in both heterologous cells and platelets, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"10627461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of the GPIbβ ectodomain reveals a single leucine-rich repeat with N- and C-terminal disulfide-bonded capping regions. A chimeric GPIbβ/GPIX structure identified a quaternary interface where GPIbβ Tyr106 inserts into a pocket formed by two GPIX loops (b,c). Mutagenesis confirmed this interface is essential for GPIb-IX complex surface expression; BSS mutations A108P and P74R maintain GPIbβ folding/secretion but abolish GPIX surface expression.\",\n      \"method\": \"X-ray crystallography of GPIbβ ectodomain and GPIbβ/GPIX chimera, site-directed mutagenesis, flow cytometry of surface expression\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with functional mutagenesis validation, multiple orthogonal methods\",\n      \"pmids\": [\"21908432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The extracellular domain of GPIbβ modulates vWF-mediated platelet adhesion. An anti-GPIbβ monoclonal antibody (RAM.1) mapped to the COOH-terminal leucine-rich flanking cysteine loop inhibited ristocetin-induced platelet agglutination, botrocetin-induced vWF binding, and adhesion of GPIb/V/IX-transfected cells to vWF under flow, increasing rolling velocity and decreasing resistance to detachment.\",\n      \"method\": \"Monoclonal antibody epitope mapping with synthetic peptides, western blot, co-immunoprecipitation, platelet aggregation assays, cell adhesion under flow\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional adhesion assays under flow with defined antibody epitope, single lab\",\n      \"pmids\": [\"11816713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A single missense mutation (Asn64→Thr) in the extracellular domain of GPIbβ prevents disulfide bonding of GPIbβ to GPIbα, blocks O-glycosylation and maturation of GPIbα (retaining it in the ER as ~66 kDa rather than 130 kDa), and destabilizes GPIX, demonstrating that GPIbβ has a dual role in controlling processing/maturation of GPIbα and stability of GPIX.\",\n      \"method\": \"DNA sequencing, co-expression in CHO cells, flow cytometry, confocal microscopy, immunoprecipitation, 35S metabolic labeling, glycosidase assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstitution in heterologous cells with mutagenesis, metabolic labeling, glycan analysis, and multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"12693941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The intracellular domain of GPIbβ (specifically residues Leu150–Pro170, with key residues Arg164, Leu165, Leu167, Thr168, and Pro170) is required for efficient filopodia formation upon VWF adhesion, independent of filamin A or 14-3-3ζ binding sites and independent of Ser166 PKA phosphorylation. Deletion of juxtamembrane or central segments reduced filopodia-forming cells by ~21–23%. Knock-in mice with GPIbβ intracellular deletion confirmed impaired filopodia upon VWF adhesion.\",\n      \"method\": \"CHO cell expression of GPIbβ deletion/point mutants, filopodia quantification on VWF matrix, alanine scanning mutagenesis, knock-in mouse model\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic mutagenesis confirmed by knock-in mouse model, multiple orthogonal approaches\",\n      \"pmids\": [\"19694944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of TRAF4 (residues 290–470) in complex with a GPIbβ peptide (residues 177–181) shows GPIbβ binds a unique shallow surface composed of two hydrophobic pockets on TRAF4. The TRAF4-binding motif Arg-Leu-X-Ala was identified in GPIbβ and also present in GPVI and TGF-β receptor.\",\n      \"method\": \"X-ray crystallography of TRAF4–GPIbβ peptide complex, peptide binding assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with defined binding motif, single lab\",\n      \"pmids\": [\"29073066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Anti-GPIbβ antibody RAM.1 inhibits GPIb-IX-associated filopodia formation and nearly all GPIb-IX-related signaling, while a novel anti-GPIbβ antibody 3G6 potentiates filopodia formation and GPIb-IX activation. These divergent modulatory effects of two antibodies both targeting GPIbβ indicate that conformational changes in GPIbβ underlie outside-in activation via GPIb-IX.\",\n      \"method\": \"Monoclonal antibody functional assays in platelets and CHO-Ib-IX cells, flow cytometry, filopodia quantification, affinity binding to purified GPIbβ and GPIb-IX\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal antibody modulation with functional readouts, single lab, two antibodies with opposite effects\",\n      \"pmids\": [\"33915031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A frameshift mutation affecting only the cytoplasmic domain of GPIbβ (p.Arg177Serfs*124) causes mild BSS with moderate reduction of GPIb-IX complex surface expression, but all mutant GPIbβ present in platelets is correctly assembled into the GPIb-IX complex at the plasma membrane, demonstrating that the cytoplasmic domain of GPIbβ is not required for assembly and trafficking of the GPIb-IX receptor.\",\n      \"method\": \"Flow cytometry, western blot, DNA sequencing, family segregation analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient platelets with defined mutation, flow cytometry and western blot, single lab\",\n      \"pmids\": [\"34638529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Rab5-dependent endocytosis regulates GPIbβ trafficking in megakaryocytes. Active Rab5 (Q79L) causes GPIbβ accumulation in enlarged early endosomes (phosphatidylinositol 3-monophosphate-dependent), while inactive Rab5 (N133L) causes GPIbβ plasma membrane retention. Rab5 activity modulates proplatelet formation.\",\n      \"method\": \"GFP-Rab5 wild-type and point mutant (Q79L, N133L) expression in primary murine fetal liver-derived megakaryocytes, fluorescence microscopy, transferrin internalization assay, PI3P inhibition\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined active/inactive Rab5 mutants with direct GPIbβ localization readout and PI3P dependence, single lab\",\n      \"pmids\": [\"34732055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The anti-GPIbβ antibody RAM.1 (and a Fc-devoid derivative) abolishes constitutive filopodia and significantly extends platelet life span in IL4R-IbαTg mice (which have constitutively exposed GPIbα Trigger sequence), providing causal evidence that GPIb-IX outside-in signaling through GPIbβ drives platelet clearance.\",\n      \"method\": \"Confocal microscopy of CHO cells expressing chimeric IL4R-Ibα complex, flow cytometry, endogenous platelet life span tracking with labeled anti-GPIX antibody in transgenic mice\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo platelet clearance with antibody intervention plus in vitro cellular validation, single lab\",\n      \"pmids\": [\"35305057\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Src family kinase Lyn directly binds to GPIbβ at the transmembrane/cytoplasmic domain interface (residues V144–A161). This interaction is required for both inward GPIb-IX ligand-induced intracellular signaling and outbound signals that enhance VWF-GPIb-IX interaction. An inhibitory peptide (mPLβ) targeting this site blocked GPIbβ-Lyn interaction, Lyn/SFK activation, stable platelet adhesion and aggregation, and in vivo arterial thrombosis in mice.\",\n      \"method\": \"Direct binding assay of recombinant Lyn to GPIbβ fragments, co-immunoprecipitation, inhibitory peptide (mPLβ) in platelets and CHO cells, biomembrane force probe for VWF-GPIb molecular bonding, FeCl3-induced carotid artery thrombosis mouse model, nanoparticle peptide delivery\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct binding assay with domain mapping, co-IP confirmation, in vitro functional assays, biophysical (BFP) measurement, and in vivo thrombosis model, single lab\",\n      \"pmids\": [\"41190427\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GPIbβ is a structural and signaling subunit of the platelet GPIb-IX-V complex: its extracellular leucine-rich repeat domain interfaces with GPIX (via Tyr106) and modulates VWF-GPIbα adhesion; its transmembrane/cytoplasmic boundary (V144–A161) directly binds Src kinase Lyn to mediate bidirectional GPIb-IX signaling; its intracellular region (Leu150–Pro170) drives VWF-induced filopodia and cytoskeletal reorganization independently of Ser166 phosphorylation; PKA-dependent phosphorylation of GPIbβ enhances 14-3-3ζ binding to the complex; TRAF4 binds GPIbβ residues 177–181 via an Arg-Leu-X-Ala motif to mediate ROS-linked thrombotic signaling; and GPIbβ is essential for proper GPIbα glycosylation/maturation and GPIX stability, though its cytoplasmic tail is dispensable for GPIb-IX complex assembly and trafficking.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GPIbβ is a structural and signaling subunit of the platelet GPIb-IX-V adhesion receptor that couples von Willebrand factor (VWF) binding to cytoskeletal reorganization and intracellular signaling [#10, #4]. Its single leucine-rich-repeat ectodomain forms a quaternary interface with GPIX through insertion of Tyr106 into a pocket built from two GPIX loops, an interaction essential for surface expression of the complex [#1], and its extracellular C-terminal cysteine-flanked loop modulates VWF-mediated adhesion under flow [#2]. GPIbβ is also required for correct GPIbα maturation: disruption of GPIbβ disulfide bonding to GPIbα blocks GPIbα O-glycosylation and ER export and destabilizes GPIX, establishing GPIbβ as a control point for processing and stability of the partner subunits [#3]. The transmembrane/cytoplasmic boundary of GPIbβ (V144–A161) directly binds the Src-family kinase Lyn to drive bidirectional GPIb-IX signaling, supporting stable platelet adhesion, aggregation, and arterial thrombosis [#10], while an intracellular segment (Leu150–Pro170) is required for VWF-induced filopodia formation independent of filamin A, 14-3-3ζ, and Ser166 phosphorylation [#4]. PKA-dependent phosphorylation of GPIbβ enhances 14-3-3ζ recruitment to the complex [#0], and a distinct cytoplasmic motif (residues 177–181, Arg-Leu-X-Ala) binds TRAF4 [#5]. Conformational change in GPIbβ underlies outside-in activation, as antibodies against GPIbβ can either suppress or potentiate filopodia and GPIb-IX signaling [#6], and this signaling drives platelet clearance in vivo [#9]. The cytoplasmic tail of GPIbβ is dispensable for assembly and trafficking of the receptor, since a frameshift truncating it still permits correct complex assembly at the membrane [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that GPIbβ's cytoplasmic domain participates in regulated 14-3-3ζ recruitment to the GPIb-IX complex, linking PKA signaling to the receptor's adaptor binding.\",\n      \"evidence\": \"GST pulldown with 14-3-3ζ, co-IP in CHO cells and platelets, truncation mutagenesis, forskolin treatment\",\n      \"pmids\": [\"10627461\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of 14-3-3ζ binding for adhesion or signaling not defined\", \"Specific phosphorylated residue not pinpointed in this study\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed the GPIbβ extracellular domain actively modulates VWF-mediated adhesion rather than serving purely as a structural scaffold.\",\n      \"evidence\": \"Anti-GPIbβ mAb (RAM.1) epitope mapping, platelet agglutination, and adhesion-under-flow assays of transfected cells\",\n      \"pmids\": [\"11816713\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single antibody, single lab\", \"Mechanism by which the ectodomain influences GPIbα-VWF binding not structurally resolved\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined a dual chaperone-like role for GPIbβ in driving GPIbα glycosylation/maturation and stabilizing GPIX, beyond its adhesion function.\",\n      \"evidence\": \"Asn64Thr mutant co-expression in CHO cells with metabolic labeling, glycosidase assays, immunoprecipitation, confocal microscopy\",\n      \"pmids\": [\"12693941\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Based on a single missense mutation in a heterologous system\", \"Does not establish whether the maturation defect generalizes to other GPIbβ lesions\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapped a discrete GPIbβ intracellular segment (Leu150–Pro170) required for VWF-induced filopodia, distinguishing this signaling output from filamin A, 14-3-3ζ, and Ser166 phosphorylation.\",\n      \"evidence\": \"Alanine-scanning and deletion mutagenesis in CHO cells with filopodia quantification, confirmed by knock-in mouse model\",\n      \"pmids\": [\"19694944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector that binds this segment to drive cytoskeletal remodeling not identified\", \"Quantitative effect modest (~21-23% reduction)\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified TRAF4 as a direct cytoplasmic partner binding a defined GPIbβ Arg-Leu-X-Ala motif, providing a structural basis for a TRAF4-linked signaling branch.\",\n      \"evidence\": \"X-ray crystallography of TRAF4(290-470)-GPIbβ peptide complex and peptide binding assays\",\n      \"pmids\": [\"29073066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional/thrombotic consequence of the GPIbβ-TRAF4 interaction not demonstrated in this study\", \"Binding shown with peptide, not full-length receptor in platelets\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Solved the GPIbβ ectodomain and GPIbβ/GPIX interface structures, revealing Tyr106 as the key contact required for GPIb-IX surface expression and explaining how some BSS mutations fail despite preserved folding.\",\n      \"evidence\": \"X-ray crystallography of GPIbβ ectodomain and GPIbβ/GPIX chimera with mutagenesis and surface-expression flow cytometry\",\n      \"pmids\": [\"21908432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not address dynamics of complex assembly in megakaryocytes\", \"Stoichiometry of GPIbβ within the full complex not resolved here\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrated that GPIbβ conformational change underlies outside-in GPIb-IX activation, since antibodies to GPIbβ can either suppress or potentiate filopodia and signaling.\",\n      \"evidence\": \"Reciprocal anti-GPIbβ mAbs (RAM.1 inhibitory, 3G6 potentiating) in platelets and CHO-Ib-IX cells with filopodia and activation readouts\",\n      \"pmids\": [\"33915031\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural nature of the proposed conformational change not visualized\", \"Single lab, antibody-based inference\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed the GPIbβ cytoplasmic domain is dispensable for receptor assembly and trafficking, separating its signaling roles from its structural assembly role.\",\n      \"evidence\": \"Patient platelets with p.Arg177Serfs*124 frameshift analyzed by flow cytometry, western blot, and family segregation\",\n      \"pmids\": [\"34638529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family/mutation\", \"Does not quantify the signaling deficit caused by tail loss\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Established Rab5/PI3P-dependent endocytosis as a regulator of GPIbβ trafficking and proplatelet formation in megakaryocytes.\",\n      \"evidence\": \"Active/inactive Rab5 mutants (Q79L, N133L) in murine fetal-liver megakaryocytes with fluorescence microscopy, transferrin assay, PI3P inhibition\",\n      \"pmids\": [\"34732055\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between Rab5 machinery and GPIbβ not defined\", \"Performed in murine megakaryocytes, single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided causal in vivo evidence that GPIb-IX outside-in signaling through GPIbβ drives platelet clearance.\",\n      \"evidence\": \"RAM.1 antibody and Fc-devoid derivative in IL4R-IbαTg mice with platelet life-span tracking, plus CHO cell chimera assays\",\n      \"pmids\": [\"35305057\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relies on a transgenic constitutively-activated model\", \"Downstream clearance effectors not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified Lyn as a direct GPIbβ transmembrane/cytoplasmic (V144-A161) partner mediating bidirectional GPIb-IX signaling, and validated this interface as an antithrombotic target.\",\n      \"evidence\": \"Direct recombinant Lyn-GPIbβ binding with domain mapping, co-IP, inhibitory peptide (mPLβ), biomembrane force probe, and FeCl3 carotid thrombosis mouse model\",\n      \"pmids\": [\"41190427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Lyn binding integrates with the Leu150-Pro170 filopodia segment and TRAF4 branch is unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GPIbβ's distinct cytoplasmic interactions (Lyn, TRAF4, 14-3-3ζ) are coordinated into a unified bidirectional signaling output, and the structural basis of the activating conformational change, remain to be integrated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the full-length GPIbβ cytoplasmic tail with its partners\", \"Hierarchy/timing of Lyn vs TRAF4 vs 14-3-3ζ engagement unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [10, 6]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 7]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [2, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 0]}\n    ],\n    \"complexes\": [\"GPIb-IX-V complex\"],\n    \"partners\": [\"GP1BA\", \"GP9\", \"YWHAZ\", \"TRAF4\", \"LYN\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}